1. Field of the Invention
The present invention relates to a wireless communication device and a metal article, and in particular, relates to a wireless communication device used for a RFID (Radio Frequency Identification) system and a metal article including the wireless communication device.
2. Description of the Related Art
In recent years, as an information management system for articles, there has been put into practical use an RFID system in which communication is established between a reader/writer generating an induction magnetic field and an RFID tag (also referred to as a wireless communication device) attached to an article on the basis of a non-contact method utilizing an electromagnetic field and predetermined information is transmitted. This RFID tag includes a wireless IC chip that stores therein the predetermined information and processes a predetermined wireless signal and an antenna (radiator) that transmits and receives a high-frequency signal.
As an RFID tag that is operable even if it is disposed in proximity to a metal plate, a metal-compatible tag described in Japanese Unexamined Patent Application Publication No. 2007-272264 is known. In this metal-compatible tag, a loop antenna conductor is wound around a plate-shaped dielectric member and an RFID chip is mounted in a gap portion formed in a portion of the loop antenna conductor. In addition, a gap is also formed on a surface side opposite to the chip mounting surface of the loop antenna conductor. When this metal-compatible tag is stuck to a metal plate, a high-frequency signal current flows in both the loop antenna conductor and the metal plate through capacitive coupling between the conductor of the back surface of the dielectric member and the metal plate.
In the metal-compatible tag, while a radiation gain on the front surface side (tag mounting surface) of the metal plate is secured to some extent, there is a problem that a radiation gain on the back surface side of the metal plate is small and a communication distance is short. That trend becomes more noticeable with an increase in the thickness of the metal plate, and, for example, it has been hard to use the metal-compatible tag for a metal article such as a stepladder, a building material, or the like.